Comparison of Formalin-Induced Porcine Ureteral Strictures with Human Ureteral Strictures

We induced ureteral strictures in pigs using 4% Formalin. In all cases, a stricture occurred with fibrosis of the muscular wall of the ureter; the lumen was preserved in most cases although narrowed. All animals developed hydronephrosis. The animal strictures were compared histologically with surgically excised human strictures. A chronic inflammatory infiltrate was noted in most of the human specimens that was not seen in the animal model. Endoscopic treatment of the animal strictures had variable results comparable to those in human strictures similarly treated. Autopsy examination of the endoscopically treated animal ureters showed fibrosis with chronic inflammation. The animal model showed variable degrees of fibrosis similar to that seen in human strictures, and dilation likewise had similar results. The fibrosis that remained after dilation was coupled with inflammation possibly secondary to the ureteral manipulation.